Reservoir for the underground storage of liquefied gases

ABSTRACT

989,218. Storing liquefied gases. CONCH INTERNATIONAL METHANE Ltd. March 2, 1964, No. 8700/64. Heading F4P. An underground rock cavern 3 in which is stored liquefied gas e.g. natural methane has a thermally insulated false roof 12 between the normal liquid level and the roof proper 13 from which extends a vertical shaft 4 and the vapour space between roofs 12, 13 is heated so as to maintain the temperature between minus and plus 20‹ C. thereby minimizing roof fracture due to temperature fluctuations. The roof 12 is of sheet aluminium or stainless steel covered with fibre glass, foamed polyvinyl chloride or foamed polyurethane and the vapour space is heated by vapour of the gas being stored. A blower 17 draws from a pipe 22 in the shaft 4 and delivers through a heater 18 into a pipe 19 and through orifices 21 in a header 20. Liquefied gas is discharged by a pump 10 through a pipe 9. In a modification the heated vapour is circulated in a closed system.

Oct. 4, 1966 J. M. SOESAN RESERVOIR FOR THE UNDERGROUND STORAGE OFLIQUEFIED GASES Filed Jan. 7, 1965 C harge Line Discharge Line FIG.

FIG. 2.

H II

INVENTOR Joseph M. Soesan ATTORNEY United States Patent 3,276,213RESERVOIR FOR THE UNDERGROUND STORAGE OF LIQUEFIED GASES Joseph M.Soesan, Cobham, Surrey, England, assignor to Conch International MethaneLimited, Nassau, The Bahamas, a Bahamian company Filed Jan. 7, 1965,Ser. No. 424,078 Claims priority, application Great Britain, Mar. 2,1964, 8,7 00/ 64 13 Claims. (Cl. 62-45) This invention relates toreservoirs for the storage of liquefied gases at low temperatures, i.e.,temperatures below -20 C.

The storage of liquefied gases in underground caverns has already beenproposed and is in wide-spread use when the gases are stored underpressure at ambient tempenature. However, the storage of liquefied gasesat low temperatures, i.e. below 2() C. at substantially atmosphericpressure is a more difiicult operation because of the low temperatureeffects on the earth formations surrounding the cavern and the shaftextending from the cavern to the surface of the earth. It is obviouslyideal if earth formations, which are completely impervious to liquidsand 'which will withstand the low temperatures without cracking, areavailable but this is very rarely the case. Certain earth formations,such as limestone, shales and granite and rock-salt are substantiallyimpermeable to liquids and, if they contain cracks, these cracks can besealed before the reservoir is put into use and so produce a perfectlyimpermeable natural cavern. However, when filling such a cavern withvery cold liquids, there is a tendency for fissures and cracks to openup in the rock due to differential contraction of the materials makingup the rock formation. When such fissures and cracks open up in the sidewalls or base of a cavern they are not normally serious because they donot result in any substantial spalling of the rock, and the fissures andcracks themselves are normally sealed by freezing of the ground waterthat enters them. However, the formation of such fissures and cracks inthe roof of a rock cavern can lead to series and unpredictable results.Unless the cavern roof is supported, these fissures and cracks canresult in serious spalling of rock from the roof, a process which can goon until there is a complete subsidence of the upper earth formationsinto the cavern. It is true that this spalling can be prevented bysuitable supporting structures but, in caverns of very substantialdimensions, such supporting structures are Very expensive to build andmaintain.

It has now been found that, if, in accordance with the presentinvention, steps are taken to maintain the roof of the cavern rat atemperature above 20" C., the danger of smiling from the roof issubstantially eliminated. This can be done in any suitable way whichwill supply heat from an external source to maintain the rooftemperature above 20" C.

However, a preferred form of the present invention provides a reservoirfor the storage of liquefied gases at temperatures below -20 C.comprising an underground cavern in a rock formation, a shaft extendingfrom said cavern to the surface of the earth, a thermally insulatedfalse roof extending over the cavern below the rock roof of the cavernand heating means for maintaining a temperature of above -20 C. in thespace between said false roof and said rock roof.

A further difficulty in connection with underground caverns for storingliquefied gases at low temperatures, arises in connection with the shaftwhich extends from the cavern to the surface of the earth in whichgenerally all necessary piping arrangements will lead down into thecavern. In order to keep ground water from flowing 3,276,213 PatentedOct. 4, 1966 into the shaft, it is generally necessary to line the shaftat least down from the surface until a liquid impervious ground layer ismet. While such a lining works quite efficiently when the liquefiedgases are stored at ambient temperatures, difficulties arise when theseliquefied gases are stored at very low temperatures. Since the shaftnormally forms part of the vapor space above the cavern reservoir, itwill be subjected to these low temperatures and, owing to differentialexpansion and contraction between the shaft lining and the surroundingearth formations, gaps will open up which will permit leakage of gasfrom the reservoir.

The present invention also meets this difliculty since the heating meansused for maintaining a substantially atmospheric temperature in thespace between the false roof and the rock roof of the cavern may, at thesame time, be used [for maintaining such a temperature throughout thelength of the shaft.

The present invention is particularly suitable for the storage of thefollowing gases, stored at their boiling point at about atmosphericpressure, the temperature of which boiling point is given after each ofthe materials listed:

Methane l6l Ethylene --104 Ethane -89 Propylene 48 Propane 42 Ammonia 33Oxygen -183 Nitrogen 196 Hydrogen 253 Helium 269 The underground cavernused in this invention may be either a naturally occurring one or may beexcavated from living rock. Any local permeabilitics in the rock can besealed off by concrete or other suitable sealing compounds or, if theflow of ground water into the cavern is not a great quantity, one canrely on the cold product to be stored in the reservoir to freeze thewater in local permeabilities and so automatically seal the cavern. Alined cavern will not generally be necessary unless the product to bestored therein has to be subjected to rigorous exclusion ofcontaminants, for example liquid hydrogen and liquid oxygen. In suchcases a cheap lining of metal or a suitable plastic may be used. Thislining need have no structural strength for its sole purpose is toprevent contamination of the stored products.

The shaft extending from the cavern to the surface of the earth issealed at the top by a metal head through which pass the various pipesnecessary for the operation of the storage reservoir, such as thecharging line, discharging line and a vapor relief line for the gasesboiling off from the stored product. It is, of course, essential toprevent the ingress of ground water into the shaft and this can be done,either by lining the shaft down to an impervious ground layer andsealing the lining into that layer or, alternatively, one can rely onmaintaining a temperature of not below 20 C. but low enough to freezethe ground water and so seal off the shaft. Even in this latter case,however, a certain amount of lining will be necessary near the surfaceof the earth so that the suitable head can be put on the shaft.

The thermally insulated false roof extending over the cavern below therock roof of the cavern is sealed into the rock wall by suitable meansand can be supported by hangers from the rock roof. The thermalinsulation may be hung below the false roof or may rest on the top ofit. Generally, the roof will be made of sheet metal capable of standingup to the low temperatures :3 involved without embrittlement, such asstainless steel or aluminum sheet. If necessary, it can be provided withsuitable expansion means, such as corrugations, in order that it can besubjected to a wide temperature range without permanent deformation.

The heating means for maintaining a temperature of above 20 C. in thespace between the false roof and the rock roof and also, where desired,throughout the length of the shaft is conveniently a flow ofcomparatively warm gas of the same type as is to be stored in liquefiedcondition in the reservoir. By using the same gas, a number ofadvantages arise. Firstly, small leakages through the false roof do notbecome important if the nature of the gas on both sides of the falseroof is the same. Secondly, the natural boil-off of the liquefied gasfrom the stored product in the reservoir can be used as a source of thewarm gas. Thirdly, when the product stored in the reservoir is acombustible gas, such as a liquefied hydrocarbon or liquefied hydrogen,the use of the same gas above the false roof minimizes the danger of theformation of explosive mixtures.

The flow of warm gas in the space between the false roof and the rockroof, and where desired the shaft, may operate in a closed system ofpipes or in free flow. Generally, the latter system is to be preferredsince it ensures maximum heat transfer and also that the spaces areswept continuously by the gas, and the leakage of contaminated gases,such as air, into the spaces is avoided. Moreover, when using free flow,it is possible to control the pressure above the false roof so that itis always slightly higher than the pressure below the false roof, thusensuring that any flow of gas across the false roof is a flow of warmgas into the reservoir rather than one of cold gas out of the reservoir,which might have adverse effects on the rock roof and the shaft. Ofcourse, it is not necessary that gas flow be used as a heating means.Suitable liquid flow, such as warm water, flowing through suitable heatexchanger pipes can be employed. Also, where there is no danger of theformation of explosive mixtures, such as in the storage of liquefiedoxygen, nitrogen and liquefied helium, ambient air can be blown throughthe space between the false roof and the rock roof and through the shaftto keep these spaces warm.

The invention will now be described in more detail with reference to theaccompanying drawings, in which FIGURES I, II and III represent crosssections through typical reservoirs constructed in accordance with thisinvention, FIGURE I representing a reservoir involving the use of freegas flow as the heating means; FIGURE II involving the use of a closedgas flow cycle for said heating; and FIGURE III showing direct heatingof the cavern roof.

Referring to FIGURES I and H, l is the ground level and 2 represents thelevel at which the sub-strata of rock are found. The ground between land 2 is water permeable. The rock below level 2 is impermeable toliquids except in local fissures and cracks, which can readily be sealedoff.

A cavern 3 exists in the solid rock and is connected to the earthssurface by a shaft 4. The cavern has been made liquid-tight by sealingoff all local cracks by suitable concrete grouting. The upper part ofthe shaft 4 is lined by a metal liner 5, which extends down into therock formation and is sealed into the rock at 6. The shaft is covered bya detachable head 7.

For filling the reservoir a charging line 8 passes through the head tothe foot of the reservoir and a discharging line 9 passes from thesubmerged electric motor pump 10 up through the shaft and out of theshaft head. A vapor discharge line 11 also passes down the shaft andstops short of the highest level to which it is intended to fill thereservoir with liquid. A plate metal roof 12 covers the reservoir abovethe highest intended liquid level and below the rock roof of thereservoir 13. This 5} false roof 12 is suitably sealed into the rock atits perimeter as at 14 and may be provided with corrugations 15 to allowit to expand and contract without any permanent deformation. This roofcan be supported from the rock roof 13 by suitable hangers 14a. Thefalse roof 12 carries a suitable thermal insulating 16. This layer maybe formed of any appropriate thermal insulating material, such as fibreglass, rock wool, balsa wood, perlite and foamed plastic, such as foamedpolyurethane or foamed polyvinyl chloride. The charging line 8,discharging line 9 and vapor relief line 11 all pass through the saidroof, the last line terminating just below the roof.

In accordance with this invention, the space between the false roof andthe rock roof 13 is kept at a temperature above 20 C. by suitableheating means. Referring to FIGURE 1, this heating means comprises a gasblower 17, a line 19, which line passes through the head of the shaftand down to the space between the false roof l2 and the rock roof 13.Before entering the shaft, the gas in line 19 can be heated, ifnecessary, in heater 18 to a suitable temperature for maintaining thedesired temperature above -20 C. in the space between the false roof l2and the rock roof 13, and the shaft 4. Heater 18 may operate on a cheapsource of heat, such as ambient air, or river water or waste gases.

The line 19, at its lower end, connects with a distribution pipe 20provided with suitable holes 21 for distributing the warm gas throughoutthe space to be maintained above 20 C. The gas flowing through thisspace exits through the head of the shaft by line 22 and hence returnsto blower 17. To make up for any gas lost in this circulating system,gas may be directed from the vapor relief pipe Ill carrying vapor fromthe liquefied gas reservoir via branch line 23 and control valve 24-.

Referring to FIGURE II, the heating system comprises the blower 17, line19 and heater 18, as in FIGURE I, but line 19 in this case is extendedinto an arrangement of the heat exchange pipes distributed around thespace to be heated, shown diagrammatically at 25, 26, and 27. After theWarm gas has circulated through this heat exchange system, it exitsthrough the head of the shaft via line 21; and so returns to the blower17. Any losses are made up from the vapor relief line 11 Via branch line23 and valve 24, as in FIGURE I.

The pipes 8, 9 and 11 may be thermally insulated above the false roof toprevent cooling of the space above the false roof by the cold fluidspassing through them.

Normally, the temperature in the space between the false roof and therock roof and in the shaft will be maintained at substantially ambienttemperature, i.e. between 0 C. and 20 C. These spaces will not normallybe kept at temperatures below 0 C. unless it is necessary, owing to theabsence of a shaft lining to freeze the ground water surrounding theshaft. In these cases, the temperature can go down to 20 C. but it isnot wise to take the temperature any further than this since, otherwise,rock spalling may occur.

The arrangements shown in the figures are particularly suitable for thestorage of liquefied natural gas and liquefied petroleum gases, but mayalso be used for any of the other gases mentioned at the commencement ofthis specification.

It will be apparent that the embodiments shown are only exemplary andthat various modifications can be made in construction and arrangementwithin the scope of the invention as defined in theappended claims,e.g., the cavern roof may be maintained at the desired temperature ortemperature range, as by embedding the heating pipes in the rock roof orvery close to it, without using the thermally insulated false roof.FIGURE III shows such an arrangement in which the lines 19 and 28 ofFIGURE II are connected to line 29, which are set directly against orvery close to the roof, and may have projections 3511 imbedded in theroof for more efiicient transfer of heat.

I claim:

1. A reservoir for the storage of liquefied gases at temperatures below20 C. comprising an underground cavern in a rock formation, a shaftextending from said cavern to the surface of the earth, a thermallyinsulated false roof extending over the cavern before the rock roof ofthe cavern and heating means supplied through said shaft for maintaininga temperature of above 20 C. in the space between said false :roof andsaid rock roof.

2. A reservoir as claimed in claim 1 in which the heating means is alsoused for maintaining a temperature of above -20 C. throughout the lengthof .the shaft. I

3. A reservoir as claimed in claim 2 wherein the temperature in thespace between the false roof and the rock roof is maintained at betweenC. and 20 C.

4. A reservoir as claimed in claim 1 in which the shaft is lined atleast down from the surface until a liquid impervious ground layer ismet.

5. A reservoir as claimed in claim 1 in which the heating meanscomprises a free flow of warm gas.

6. A reservoir as claimed in claim 1 in which the heating meanscomprises a flow of warm gas through a closed gas circulation system.

7. A reservoir as claimed in claim 5 in which the gas is the same as thegas stored in liquefied form in the reservo1r.

8. A reservoir as claimed in claim 7 in which make up for thecirculating warm gas is provided from a vapor relief line from thereservoir.

9. A reservoir as claimed in claim 7 wherein the pressure above thefalse roof is maintained slightly higher than the pressurebelow thefalse roof.

10. A reservoir for the storage of liquefied gases at temperatures below20 C. comprising an underground cavern in a rock formation, the roof ofsaid cavern being formed by a part of the rock formation and beingsubject to spalling at the low temperature of the stored liquefiedgases, a shaft extending from said cavern to the surface of the earth,heating means for maintaining the temperature of the rock roof of thecavern at above 20 C., and means extending through said shaft forsupplying said heating means with heat.

11. A reservoir as claimed in claim 10 in which the heating meansinclude means for conducting a fluid heating medium down through theshaft into heat exchange relation with the cavern roof.

12. A reservoir as claimed in claim 1, said false roof comprising ametal plate roof suspended from the rock roof of the cavern by hangers,a layer of insulation supported on said plate roof, said heating meansbeing between the insulation and the rock roof, filling and dischargepipes for stored liquid extending from the surface of the earth throughsaid shaft and through said false roof, means for circulating heatexchange fluid through said heating means and means at the surface forheating said fluid.

13. A reservoir as claimed in claim 12, said fluid being the samematerial as the liquefied gas which is stored, but in gaseous form, avent pipe extending from the vapor space immediately beneath the falseroof to the surface, and a valved connection between said vent pipe andsaid heating means for supplying said heating means with gas from saidvent pipe.

References Cited by the Examiner UNITED STATES PATENTS 2,437,909 3/ 1948Cooper 62-45 2,707,377 5/1955 Morrison 62-50 2,932,170 4/ 1960 Pattersonet al 62-45 X 3,083,537 4/1963 Dougherty 62-45 X 3,089,309 5/1963 Closset al 62-45 X 3,205,665 9/1965 Van Horn 62-45 X FOREIGN PATENTS 807,9691/ 1959 Great Britain. 969,890 9/ 1964 Great Britain.

LLOYD L. KING, Primary Examiner.

1. A RESERVIOR FOR THE STORAGE OF LIQUEFIED GASES AT TEMPERATURES BELOW-20*C. COMPRISING AN UNDERGROUND CAVERN IN A ROCK FORMATION, A SHAFTEXTENDING FROM SAID CAVERN TO THE SURFACE OF THE EARTH, A THERMALLYINSULATED FALSE ROOF EXTENDING OVER THE CAVERN BEFORE THE ROCK ROOF